AI coding firm Cursor built its new Composer 2 model on an open-source base from Moonshot AI’s Kimi, the company acknowledged.
The revelation followed claims by an X user, impacting perceptions of the U.S. startup’s frontier-level coding intelligence model. Cursor had launched Composer 2 promoting it as offering “frontier-level coding intelligence” without initially mentioning its foundational components.
An X user identifying as Fynn stated Composer 2 was “just Kimi 2.5” with additional reinforcement learning. Kimi 2.5 is an open-source model developed by Moonshot AI, a Chinese company backed by Alibaba and HongShan.
Cursor Vice President of Developer Education Lee Robinson confirmed Composer 2 started from an open-source base.
Robinson stated approximately one-quarter of the compute for the final model originated from the base, with the remainder from Cursor’s training.
He added Composer 2’s performance on benchmarks is “very different” from Kimi’s. Robinson also maintained Cursor’s use of Kimi complied with its licensing terms.
The official Kimi account on X subsequently congratulated Cursor, noting its use of Kimi was “as part of an authorized commercial partnership” with Fireworks AI.
The Kimi account stated, “We are proud to see Kimi-k2.5 provide the foundation.” Cursor co-founder Aman Sanger acknowledged the omission, stating, “It was a miss to not mention the Kimi base in our blog from the start. We’ll fix that for the next model.”
Cursor is a U.S. startup that raised $2.3 billion in a funding round last fall, achieving a $29.3 billion valuation.
